Automatic mechanical transmission systems and the automatic controls for the master clutches thereof are known in the prior art as may be seen by reference to U.S. Pat. Nos. 3,478,851; 3,752,284; 4,019,614; 4,038,889; 4,081,065 and 4,361,061, the disclosures of which are hereby incorporated by reference.
Briefly, in such automatic mechanical transmissions systems, various drive line operations, including, the supply of fuel to the engine, the engagement and disengagement of the master clutch, the shifting of the transmission and the operation of other devices, such as input or output shaft brakes, are automatically controlled by a control system based upon certain measured, sensed and/or calculated input parameters. Typically, the input parameters include engine speed, throttle position, transmission input and/or output shaft speed, vehicle speed, current engaged gear ratio, application of the brakes and the like. The term throttle position is utilized to signify the position or setting of any operator controlled device for controlling the supply of fuel to an engine.
Referring specifically to the automatic clutch control, in a vehicle equipped with an automatic mechanical transmission, during normal operation, when starting from rest or operating at a very low speed, the master friction clutch is modulated between fully disengaged and fully engaged conditions, i.e., is partially engaged, according to certain input parameters, to maintain the engine speed at a set value above idle speed and/or to achieve smooth starts. This method of engaging the master clutch generally provides a high quality and consistent engagement of the clutch under all types of throttle applications. However, a smooth and consistent engagement of the clutch is not necessarily desirable in all circumstances, particularly when the vehicle is starting out on a steep grade or when other aggressive performance is demanded by the driver or the control system.